Radio navigation system for targets in altitude layers



May 6, 1952 P. J. HERBST 2,595,358

RADIO NAVIGATION SYSTEM FOR TARGETs 1N ALTITUDE LAYERS Filed sept. 27, 1945 2 SHEETS-SHEET 1 0 70 2000 0n-7a l Til 400070000021409@ .BY @WA l .Qi

Arm/Mir May 6, 1952 P. J. HERBST 2,595,358

RADIO NAVIGATION SYSTEM FOR TARGETs IN ALTITUDE LAYERs kBY Patented May 6, 1952 OFFICE 7 RADIO NAVIGATION SYSTEM FOR TARGETS IN ALTITUDE LAYERS Philip J. Herbst, Princeton, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application September 27, 1945, Serial No. 618,969

7 Claims. (Cl. 343-6) My invention relates to radio navigation and traiiic control systems and particularly to systems for ship or aircraft operations wherein the desired information is obtained from radar or transponder beacons interrogated by radar pulses.

' The term transponder as used herein is intended to mean a combination including a receiver designed to receive signalswhich are referred to hereinafter as interrogation or trig-l ger signals, and a transmitter controlled by the output of said receiver to transmit other signals which are called reply signals.

The invention provides means for automatirialy No. 607,9991/2, filed July 3l, 1945 in the name' of Loren F. Jones and entitled Radio Navigation ISystem. v In the Jones application there is described and claimed a navigation system' for ships' or aircraft which comprises a radar sys-.,

tem such as 'a plan position indicator system (P. P. I. system) on the ground and a television transmitter for transmitting the P. P. I. view of vcraft within the service area oi the P. P. I. and television'stations to said craft.

Each ship on.I aircraft carries a television receiver and a radar" or transponder beacon, also, if the present invention is employed. Preferably, a map superimposed on the P. P. I. view is transmitted also by the television transmitter.

l y An object ofthe present invention is to provide an improved radio navigation and/or trafc control system. v

A further object of the invention is to provide a means of separating the responses from air-l craft in dierent altitude groups in systems employing ground search radar.

A further object of the invention is to provide a, combined radar and television navigation system having improved means fortransmitting 'to aircraft ina particular altitude layer a P. P. I. or other radarpicture of only the aircraft within a certainV altitude layer or altitude range.

A still further object of the invention is to providewin a radar navigation or control system an improved method of and means for distinguishing between aircraft flying in different altitude layers and providing such separation of data, for the simplication of traffic control procedures.l I

The invention will be described by way of eziample as applied to a system similar to thatA described in the above-mentioned Jones application wherein the ground station comprises a P. P. I. system which radiates radio pulses from a, directional antenna that is continuously. rotated through 360 degrees to search for aircraft in the vicinity. A cathode ray indicator tube is provided with a deiiecting yoke that is rotated in synchronism with the antenna, and the cathode ray is simultaneously deflected radially at a comparatively rapid rate in synchronism with the pulse transmission. Radio pulses reflected or retransmitted from said aircraft are picked up by said antenna and caused to modulate the cathode ray. Thus there appears on the cathode ray screen a View wherein a spot on the screen corresponds to a particular aircraft, and wherein the aircrafts position with respect to the P. P. I. antenna is shown. This view is'transmitted by a television transmitter so that it may be received by any aircraft within the service area that'is-equipped with 'a television receiver. Since the P. P. I. picture Ymay show a plurality ofV aircraft in the service area, suitable means is' provided to show a pilot or navigator which one of the spots in the picture is the one corresponding to his airplane.

Each aircraft carries a radar "pulse repeater unit which is referred to as' a' radar beacon or 'transponder beacon. Each transponderfbeacon transmits two puses in response' to interrogation by the ground search radar station, 'that is, in response to the reception of a pulse bythe P. P. I. station. The two pulses thus transmitted are separated by a code time interval, a particular code interval being assigned to a certain group of aircraft. In the example being described, the aircraft flying in a particular altitude layer such as fromO to 2000 ft. are assigned one code delay time while those in a different altitude layer such as from 2000 to 4000 ft. are assigned a different code delay time. At the ground radar station suitable means, is provided for causing signal of a particular code delay to appear on a preassigned indicator tube screen.

The inventionwill be betterunderstood from the following description ltaken inv connection with the accompanying drawing in which A Figure l is a block diagram illustrating one embodiment of the invention,

Figure 2` is a block diagram of a system that may be carried by an aircraft .which 'is to use the ground station of Fig. 1 for navigation, and

Figure 3 is a group of graphs illustrating the operation of the system shown in Figs. 1 and 2. In the several figures, similar parts and graphs are indicated by similar reference characters.

Referring to Fig. 1, the ground station com- K prises a radar system of the P. P. I. type which The cathode ray indicator tube Iimay .be of.

conventional design having a control grid I3 to whichpulses from the Y'receiver I3 are applied. `'lhe pulses are supplied-from the-'receiver I3 to the ,grid I9 through the `conductor i4 land througha decodirigdelayrietworkl 20 and a'mixer .and clipper circuit 25, described hereinafter. The cathode ray is de'ected `radially by means of a deflectingvyoke'ZI comprising apair of deflecting coils and provided with 'conductor .rings 22 and brushes23 whereby vthe yoke'ZI may be rotated during 'the radial deection. A sawtooth deflectying wavev 'is suppliedlto the deflectingJyoke 2l Afr om a sawtooth Ideection circuit -24. The deflection .circuit-f2.4 issynchronized with lthe pulse transmission :by .means .of pulses 4taken off .the .pulse .transmitter .II and supplied over .conductorsl `and .througha delay'netwoi-k 2lV to j ,the circuit 2,4. The delay network 213s employed todelay the start of vlthelcathode ray .sweep at the tube I5. The amountv of this delaydepends on the coding delay assigned to ,the aircraft.' flying ina particular altitudelayerand which yare v -to-.be Vindicated on the vcathoderay tube LIS. .In the example being ',descr-ibed, the .indicator .tube -IG-shows'the aircraftinthe 0-.2000 vfoot altitude layer.

Amotor28 is mechanically-coupledlto the antenna 'I0 .and tto' the .yoke 2| .for frotating them hin synchronism atxsome -s1ow rate such as one rotationevery sixseconds.

- .The y*cathode ray tube lvfisrprovided with a .phosphorescentscreen 3 I` having long persistence. Light vspots appear onthe `screen .3,I, as in the usualP.,LP. I.;picture, Whichnorresponds to the lfaircraft that 'reflect or 'retransmit the radio pulses. Y.Also,.;a Vrotating radial line or marker. linemay beimade to :appear on thescreen 3|.`

Aspot in the P. :P. I. picture corresponds to van aircraft, the distance of the spot from the center of vthe picture 'showing the distance from the Vradar station `to said aircraft, andthe angular- .position Jof'the spotshowing the azimuth ofthe aircraft 'Withrespect .tothe radar station.

The P. P. I. picture on the screen A3l is picked -up'by a television camera 32 of 'a conventional type including ari Iconoscope or Orthicon and is,`

transmitted from 'fan antenna 33 which, in Ythe present example,`is non-directive. The television transmitting system is of conventional design and comprises, in addition to the television 'camera 32, suitable amplifiers and mixers indiand aradio transmitter 3l that Ytransmits a carkso these pulses appear at the output of the receiver v rier wave modulated bythe usual mixture ofI pictureand synchronizing signals.

A map 38 of the territoryl surrounding the ground station preferably is superimposed on the P. P. I. picture and transmitted therewith. The map may be drawn on transparent material and suitably' illuminated.

'Referring n'oW'to theaircraftjequpment, each aircraft is provided with a radar beacon, also referred. to as a transponder beacon, that receives :.thetgroundstationpulses on the carrier frequency "f1 :and Yretransmits pulses on the carrier frequency f2 as indicated in Fig. l. Each aircraft is'also'provided with a television receiver which isituned. tothel carrier frequency assigned to the particular altitude layer in which the aircraft -isiiyingzasindicated in Fig. l. This aircraft beacon equipment is shown vin detail in Fig. 2 vand will be described with reference to Fig. 2 hereinafter. As illustrated in Fig. l, the aircraft inith'eSO-QDOO layer'receivesxapicture thatis a duplicate of .fthe :combined '-v-view of the P. P. VI.

; picture of :'tubegI 6 and .the mapx38, this composite Vpicture :being transmitted -at :the carrier Vfrequency f3. The-.spots .in the received ,picture correspond to the spots on the P. P. I. screenf3l which vare'.representative of' aircraft. Therefore, the v:pilot-of an aircraft-'canfsee his :location with respect to `ithe airport-:and with rrespect to anything :elsegshownpn vthe mapproviding he can determineswhat: spot i-n the-RP.; I. picturezcorre- Asrzon'dstoIhisown:aircraft eSuitable means vfor obtaining such .aire-raft'identification YWillbe describedfhereinafter. p

.ReferringLto 2,:theziradargbea'con.carried-by 2eachzaircraft;comprisesfaradiopulse. receiver A'4 I which.receivesfandfdemodulates theradarpulses transmittedfrom the groundstation on a carrier Wave .frequency fr.. .The '.dcmodulated pulses shown ipby fthe graph 143 Vrmay be .sent through `a :delayline :or tn etwork :'42 and f the resulting de- `layed 'pulses :shown by-tlrexgraph -fl are applied as modulating ;.pulses to--arradio :transmitter 43 operating, on 1a -carrier wave Yfrequency f2. 'The .demodulated `pulses A:are 'also applied by way 'of :a branchzcircuit .through adelay network: 44 to obtain the e'delayedgpulses show-nby .the igraph 41 which are'also Aapplied vas :modulating pulses to the 'transmitter-d3. eAsshown by `the graph 48, the pulses 45:1and flappear'as pairsofpulses `at `the input -of transmitter 43 to 4providepulse time coding. Thusfeach .pulse'receivedfat the beacon,isretransmittedxas apairof pulses -at the carrierfrequency fa The delay introduced by the network 42 and thedifference in thefrequencies f1 and fzare utilized to-.prevent .singing of the beacon circuit. As -will be explained hereinafter, the delay network 421may be vomitted if desired. The vdelay introduced bythe network 44 is utilizedfor 4coding purposes, `a particular coding delay being 4.assigned .for Y.each altitude layer. These altitude layers andthecorresponding code delaysmay,. for.- example, `be. as .followsz 0 to"2000'ft.'25 as. code delay. '2000 ft. to 40005ft.35 as. code delay. A4000 ft.'to 6000 fin-:45 as. 'code delay.

The graphs in Fig. -3 illustrate the method of decodingfthe retransmitted signals at the ground station. If an aircraft ying at an altitude vof less than 2000 feetreceives ypulses from v"the ground station, thefaircraft beacon' transmits the pairs of pulsesrepresentedby`graph 48a, and

I3. It is assumed for the purpose of illustration ,lfnthere is an aircraft in thel 2000 atomes 'The pairs of pulses 48a are applied from the receiver I3'to the decoding delay'network 20 andk to the vacuum tube 5| of the mixer-clipper circuit 25. The pairs of delayed pulses 48a 'is of `greater amplitude than the others since "the" decoding delay of as. has caused the first vpulse of graph 48a to occur simultaneously with the'second pulse of graph 48a. Only the top 'portion of this high amplitude pulse is passed through the mixer-clipper 'circuit 25 to the grid AI9 of the'cathode-ray indicator tube I6, this being accomplished by adjusting the bias on the tube V55 tocmake it clip or limit at the level indicated by the dotted line 54. Preferably, the radio receiver "I3 is adjusted to limit the amplitude of the pulses before they are applied to the Vmixer-clipper circuit 25 so that there is no'pcssibility` of the lower amplitude pulses ofv Athe graph 48a" passing through the circuit 25. It will be apparent that the start of the radial deflection' of the cathode ray in the tube is' -.should be delayed by substantially the saine amount l,that the pulse appearing on'the'grid I9fhas" been delayed by the Ydelay network. Othervlwise, the spotl produced on the screen 3| bythe pulse would not appear at the correct distance' from the center of the screen to( indicate the distance to the aircraft, or it might not appear on the screen at all. For this reason, the delay networkor circuit 21 delays the sawtooth wave triggering pulse by an amount equal to the cod- -ing Idelay,.which in this instance is 25 frs. As previously stated, the viewof aircraft in, the ,0. to 2000 ft. layer thus obtained on the screen 3 I is televised to said aircraft on the carrier waveucf frequency f3. Since the televisicni'-j ceivers on aircraft or other altitude layersmare tunedto frequencies other than fa they will not receive thepicture on screen 3|.

to 4000 ft. layer, its beacon will transmit pairs of pulses with a code delay of as. as shown at 48A in Fig. 3. These pulses will produce no indication at theindicator tube I6 because the decoding networkf- ZU delays them only2'5 as.. as shown at .48B so that no pulses are superimposed or added. Likewise, as will be apparent from thefollowing description, the pulses 48a from the 0 to 2000"ft. layer will not affect the indicators l1 and I8 for the other altitude layers.

. Referring now to theindicator and television circuits for the 2000 to 4000 ft. indicator I 'Ifr and 4ior the 4000 to 6000 ft. indicator at I6, the parts corresponding to those for the 0 to 2000 ft. indicator vI 6 are indicatedgby .Similar reference numbers .with the sufxes A and B, respectively.

.,: -If an aircraft in the 2000 to 4000 ft. layer receives radio pulses from the ground station,

-the radar beacon on said craft retransmits pairs of pulses with a code delay of 35 as. as shown at 48A in Fig. 3. These pulses are supplied fromV theffdelay network 20 are applied to the vacuum tube 52 of the mixer clipper-circuit 25.

6 from the ground station receiver I3 to the delay network 20A and to the mixer-clipper circuit 25A whereby a pulse is applied to the indicator tube I1. This action is the same as previously 'described with reference to the operation of the indicator tube I6. Specifically,l the decoding network 20A delays the Apiilses 48A to produce the delayed pulses 48A `which are applied-Cto" the mixer-clipper circuit 25A."The pulses 48Aa`i`e also applied, without being delayed, to the circuit 25A so that the pulses 48A and 48A add as shown at 48A". Only the high'amplitude pulsewhich results is applied to the grid of the indicator tube I1. Thus, only retransmitted pulses from the aircraft in the 2000 to 4000 ft. layer produce an indication on the tube I'I, and only these aircraft appear on the Vpicture produced on the screen 3| A. This pictureis televised on the carrier Wave of frequency f4 to the aircraft inthe `2000 to 4000 ft. layer only.

In the same way, the retransmitted pairs of pulses 48B (Fig. 3) from the aircraft in the 4000 to 6000 ft. layer produce a pulse on the grid I9B of the indicator tube I8. This is illustrated in Fig. 3 where the pulses 48B are delayed by the decoding network 20B to produce the 1delayed pulses 48B'. The pulses 48B and the undelayed pulses 48B are added in the mixerclipper circuit 25B, as shown at 48B", whereby a large amplitude pulse is obtained which passes through the circuit 25B to the grid ISB. It will be evident that pairs of pulses from other altitude layers will not produce any indication on theindicator tube I8. The resultingfpicture on the screen 3IB showing aircraft in. the- 4.000 to 6000 ft. layer is televised to thesel aircraft only on the carrier wave of frequency f5.

It will be apparent; from the foregoing that when an aircraft ascends or descends into `a .different altitude layer, the coding delay introduced by the delay networkor circuitv (network 43 in Fig. 2) should be changed. Preferably this is done automatically by a barometricaltimeter which is indicated at- 6I in Fig. V2. The altimeter shaft 62 assmes an ,angular position which is a function of altitude. The shaft 62 is vmechanically coupled, as indicated. byv ythe broken line 63, to a rotatable switch shaft4 at vvthe delay network 4.4, Rotation offthehshaft 64 switches the ldesired number ofl delay. line sections intothe circuit in steps, there being lone switching step foreach altitude layer.

As described in the above-identified Jones application and as indicated in Fig. 2, it is also desirable to have an altimeter, such as the altimeter 6I, automatically change the tuning of the television receiver 66 on the aircraft in response tovsaid aircraft going to a diierent altitude layer.

At an aircraft a pilot Vmay determine which spot in the received-picture represents his aircraft by closing momentarily the key (il Fig.`:2 r) at the pulse transmitter 43 to increase orinter-l rupt the transmitter power output. This will cause the said spot either to brighten momentarily or to disappear momentarily as the case may be' `.i

If the delay network 42 is employed as shown in 2, it is advisable'to provide at theground radar receiver a delayzcorrection such as a cor.-

neonazis geitherzshipsv or aircraft lwherein `differenttrans- .fponder :codes sare assigned fto Hcraft 1 at different #distances respectively; from the ground search `1a dar. Also, 'it' will 4be apparent `*that for tsome applications Aof` .theinvention,fthe television equip- Ament; ,may be omitted. since .an operator at `the ground s tation:may give instructionsgto theicraft .-by"-means .of the usual radio communication fieguipment. l f I claimfas my invention: A

,1. In combination, zalgcontrol. station comprising a pulse transmitter yand-1a pulseireceiver, kapluirality-.of .receiver-transmitter unitsfor transmit- Atingssignals in response .to;receptionof signals from'-,saidrpulse transmitter, means for modulat- `,ingsaidlsignalstransmitted from said units with different modulation signals assigned to different units,'eachsaid modulated signal comprising two pulses nWhichare spaced by Va predetermined assigned time interval,` lsaid pulse receiver includring-.aplurality :of indicators vand modulation relfsponsive 'means for veach of i said indicators, said .modulation responsive\ means :including #means oriidelaying said modulated: signal in Aone Vchannelf-byanamount substantiallyequalrto'the char- :Lacteristic time interval of the desiredsignal, said modulation responsive :means furtheriincluding ineans for-.addingthe delayedimodula'ted 'signal from said-'one channelzand' theundelayed moduystation signals in response-to reception ofisig-nals ftransmitted by said'groundstation, .means for fmodulat'ing said lietransmitted-signals with ka dif- `2-ferent modulationsignal `assigned to each of said altitudelayers, each modulated signal comprising twopulses which a-r-e spaced by a predetermined assigned time interval, said locator system including av separate cathode ray tube indicator for each of said altitude layers and modu- 'lation responsive means for each of said indicators, said modulation responsive means'includingmeans for delaying said modulated signal in onechannel by an amount substantially equal to said time interval, said modulation responsive means further including means for adding the de- "layed modulated signal from said one channel and the undelayed modulated signal from a second'channel ,whereby the first and second pulses *from* said one channel and said second channel, respectively, addv to produce a combined'pulse of f gjincreasedamplitude.

I' 3. A navigation system for aircraft Within the servicearea of-a 4ground station which are to iiy iinjpreassigned altitude'layers, said system cornprising a ground station which includes a radio locator system for obtaining the distance and azimuth of each of said aircraft, a transponder or repeater unit carried by each aircraft for re- 8 ceiving and retransmitting ground stationgsigna1s,.` means.` for `pulse time code modulating .the

retransmitted transponder signals withgaidifferent lmodulation Vsignal-assigned vto eachofxsaid altitudeI layers, receiving means also.-carriedby each of .saidiaircraft vfor receiving. said .distance l and. azimuth information signals, means carried by eaphotsaid aircraft for reproducingisaid distance and azimuth .signal informationas apicture image having spotstherein showing the Apositionsvofvsaid aircraft with` respectito saidg'round station, ,and means, for identifyinglatA an=.a,ircraft Vthaspo tlin.said picture image -Whicncorresponds to saidaircraft, said,radiolocatorlsystemlinclud- `ingffa .separate .receiver channel for each of .said

:alAti'tude` layersv and inodulationlresponsiv'e means foreach of said channels, and transmittingmeans .for transmitting `on separate., channels the'iinfor- .mationappearing attheoutputs of saidchannels, respectivelmto th'e aircraft inj'said different altitudelayers',. respectively.

-.4...ln anaircraft. navigation systemvfor .aircraft that `are tofiy in preassigned altitude flayersva 1- ground station comprising a radiolocator system .of the plan-position-indicator type forproducing .forpulse time code modulatingtne retransmitted :transponder signals with Va 'different modulation ,signal assigned to each of said altitude`..layers, said ,radioQlocator system including a separate picturereproducing.indicator vfor each of i said altitude. layers and` modulation responsive means foreach of said indicatorsysaid television system including means for transmitting 'on 'separate channelsjthepictures `appearing on each of' said indicators, respectively, to the aircraft in saiddifferentialtitude layers, respectively.

5. The system according'to claim"4wherei n means including an altimeterr is carriedf by each of said aircraft for Vchangingthe modulation of the transponder;retransmitter and for `also Ychanging Ithe tuning of thevtelevision receiver on theaircraft in response to said aircraft 'flying from one of s aid 'altitude layers toV a different altitudela'yer.V

6. In a navigation system for'aircraft that are .to ily in preassigned` altitude layers, each aircraft carrying a television receiver for receiving; signals representative of a radio locator picture andv a map which are transmittedfrom 'a ground station and for reproducing said picture and -said map as a composite, picture havingspotssuperimposed on-said map showing the positionsfof radio 'locator 'system forobtaining the* distance andazimuth of each of said aircraft` and for 'producing a 'picture hav-ing rspots therein locatedn v'acc or'daric'e tvi'tlisaid distance andazimutnfinformation andshowing the'positionsofsadaircraft,

fsaid radio locator system including a separate picture-reproducing indicator foreachof said fal- V'titude layers and modulation responsive 'means portion of the service area of said ground station.

7. In an aircraft navigation system for aircraft that are to fly in preassigned altitude layers, a ground station comprising a radio locator system of the plan-position-indicator type for producing a picture having spots therein showing the positions o-f said aircraft with respect to the ground station, a television transmitter system for transmitting said picture to said aircraft, a transponder or repeater unit for receiving and retransmitting signals transmitted from said ground station and a television receiver which are carried by each o-f said aircraft, means for modulating said retransmitted signals with a different modulation signal assigned to each of said altitude layers, each modulated signal comprising two pulses which are spaced by a predetermined assigned time interval, said locator system including a separate picture reproducing indicator for each of said altitude layers and modulation responsive means for each of said indicators, said modulation responsive means for each indicator including means for delaying the modulated signals in one channel by an amount substantially equal to the time interval assigned to the altitude layer for which the indicator is to produce indicationsand further including means for adding said delayed modulated signal from said one channel and the undelayed modulated signal from a second channel whereby the rst and second pulses from the two channels, respectively,

add to produce a combined pulse of increased amplitude, said television system including means for transmitting on separate channels the pictures appearing on each of said indicators, respectively, to the aircraft in said different altitude layers, respectively.

PHILIP J. HERBST.

REFERENCES CITED The following references are of record in the Number Name Date 1,894,019 Buckley Jan, 10, 1933 2,027,530 Hammond Jan. 14, 1936 2,134,716 Gunn Nov. 1, 1938 2,252,083 Luck Aug. 12, 1941 2,307,029V Elm Jan. 5, 1943 2,312,203 Wallace Feb. 23, 1943 2,401,432 Luck June 4, 1946 2,403,603 Korn July 9, 1945 2,459,811 Grieg Jan. 25, 1949 2,468,045 Deloraine Apr. 26, 1949 2,513,282 Busignies July 9, 19504 FOREIGN PATENTS Number Country Date Great Britain Aug. 3, 1943 

